Understanding Air Quality and Temperature Control Inside Airplanes

James Hernandez

Updated Thursday, June 13, 2024 at 7:30 PM CDT

Understanding Air Quality and Temperature Control Inside Airplanes

Air Quality Inside and Outside the Plane

The air inside a plane and the air outside at cruising altitudes are fundamentally different in terms of density and breathability. At high altitudes, the outside air lacks sufficient oxygen for human survival. Passenger planes are not fully airtight ecosystems like spacecraft and submarines; they exchange air with the outside environment. This exchange is designed to be gradual, mixing warm cabin air with fresh air coming from the engines.

The air exchange rate in an airplane is significantly lower than that of an apartment with an open window, even in extremely cold conditions. This controlled exchange helps maintain a breathable atmosphere within the cabin, ensuring passenger comfort and safety. The aircraft's ecosystem is meticulously designed to balance these air exchanges, making sure that passengers receive a continuous supply of fresh air while maintaining optimal pressure and temperature.

Heat Generation and Cooling Requirements

A plane with 220 passengers produces about 22 kW of heat from the passengers alone. Sunlight streaming through airplane windows adds approximately 8 kW of heat to the cabin, while electrical systems, including lights and monitors, contribute about 19 kW of heat inside the plane. Despite the insulation, the plane loses about 17 kW of heat when the outside temperature is around -31°C (242K).

In total, the airplane needs to cool the interior by about 32 kW during flight. On the ground in hot conditions, such as in Dubai with a surface temperature of 50°C, the cooling requirement increases to about 58 kW. While planes may need heating on the ground in winter, they do not require heating while cruising due to their effective insulation.

Air Compression and Conditioning

The air used to make the cabin breathable is sourced from inside the engine, where it is highly compressed and thus very hot. Compressed air from the engine can reach several hundred degrees Celsius before being conditioned for cabin use. This hot air is then cooled down through "air conditioning packs" before being introduced into the cabin.

The process of compressing air at high altitudes, where temperatures can be around -50°C (-58°F), results in the air heating up to about 40°C (104°F). To make the air suitable for human comfort, it must be cooled down after compression. At 35,000 feet, the air pressure is only about 1/4 of sea level pressure, making it too thin for people to breathe without compression.

The Role of Turbine Engines

The turbine engine's compressor section compresses the air before it is used in the combustor, and some of this compressed air is bled off for cabin use. The raw bleed air from the engine is too hot for direct cabin use and must be cooled by the air conditioning system. The air conditioning system, known as "packs," cools the bleed air to a comfortable temperature before it is introduced into the cabin.

This sophisticated system ensures that passengers experience a comfortable environment throughout the flight, regardless of the external conditions. The continuous management of air quality and temperature is a testament to the advanced engineering and design of modern aircraft, providing a safe and pleasant journey for all on board.

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